1. Field of the Invention
The present invention relates generally to building construction. More particularly, the invention concerns a method and apparatus for post tensioning steel strands in reinforced concrete slabs.
2. Discussion of the Prior Art
In accordance with standard prior art construction techniques concrete floor slabs are typically reinforced with high strength steel strands to increase the load carrying capacity of floor slabs. Post-tensioning of these strands is also a routine engineering procedure, when the steel strands penetrate the edge of the slab and are anchored therein using a standard anchoring device.
In those instances when a post-tensioned slab design is used in conjunction with a typical prior art precast hybrid moment resistant frame that is also serving as the architectural facade of the building, it is not possible for the strand to penetrate the edge of the slab due to the architectural nature of the beam face. In this case, to still gain the advantage of the strand post-tensioning, the strand must be accessed from the top of the slab at a location far enough away from the interior beam face so as to allow for the positioning of appropriate strand stressing equipment such as a stressing jack.
In the past when a strand terminated at a point other than a slab edge, a wood frame blockout was typically constructed so that the strand could be accessed at the top of the slab. These wood frame blockouts, which are constructed prior to pouring the slab, are both labor-intensive, time-consuming and expensive to construct. Additionally, following the post-tensioning step, the relatively large cavity formed by the frame blockout had to be filled with concrete, generally by hand. This required the time consuming step of constructing and installing a bottom form and then filling the rather large cavity with concrete. It is these prior art construction problems that the method and apparatus of the present invention seeks to alleviate. As will be better understood from the description that follows, one approach to the solution to the aforementioned problems is to provide an elastomeric slab blockout assembly of unique design that is easy to install and remove and, after being removed from the poured slab, leaves a relatively small cavity that can be quickly and easily filled.
In one form of the invention the novel blockout assembly is constructed so as to have a relatively small overall height that allows it to be supported by the underlying slab reinforcement steel bars in a manner such that the top of the block out assembly is flush with the top of the slab. By not having the block out extend completely through the slab, the fill-in operation can be performed without having to construct and install a bottom form. Additionally, because the top surface of the removable blackout assembly is flush with the top of the slab elevation, the concrete finishing equipment can freely pass over the block out without interference. This eliminates the xe2x80x9crollingxe2x80x9d of the slab edge which inevitably occurs at an edge form of conventional construction.
The elastomeric blockout assembly of the invention is preferably configured to form a cavity having a length and a width that will readily accommodate the throw of the stressing jack. Because, in the preferred form of the invention the body of the blockout assembly is constructed from an elastomeric material, it can be easily flexed to expedite its easy removal from the poured slab. Additionally, the elastomeric material chosen is preferably of character that allows for easy cleaning to permit multiple re-use of the blockout assembly.
It is an object of the present invention to provide a method and apparatus for use in post-tensioning a reinforcing strand disposed within a concrete slab of the character having a plurality of reinforcing members embedded therein. More particularly, it is an object of the invention to provide an apparatus of the character described that includes a yieldably deformable elastomeric body having a top wall, a bottom wall and side walls interconnecting the top and bottom walls, the elastomeric body having a longitudinally extending passageway formed therein for receiving the reinforcing strand.
Another object of the invention is to provide an apparatus as described in the preceding paragraph in which the elastomeric body has a thickness less than the thickness of the concrete slab so that the elastomeric body can rest on the reinforcing members with the top thereof substantially flush with the top of the concrete slab.
Another object of the invention is to provide removal means for expeditiously removing the elastomeric body from the concrete slab after the slab has been poured.
Another object of the invention is to provide an apparatus as described in the preceding paragraph in which the elastomeric body is readily deformable so that, by pulling upwardly on the removal means, the body can be deformed in a manner to easily separate it from the poured concrete slab.
Another object of the invention is to provide an apparatus of the character described that is constructed of a material that is readily cleanable so that the blocking assembly can be reused a significant number of times.
Another object of the invention is to provide an apparatus of the class described herein which is easy to use, is inexpensive to manufacture and, after being removed from the poured slab, leaves a relatively small cavity that needs to be filled with concrete.
These and other objects of the invention are achieved by the method and apparatus described in the paragraphs that follow.